Hypereosinophilia and metastatic anaplastic carcinoma of unknown primary.

The differential diagnosis of eosinophilia may sometimes be difficult. Eosinophilia may occur in a diverse array of conditions from parasitic infestations to malignacies. Idiopathic hypereosinophilic syndrome has also been described. A 65-year-old male patient presenting with eosinophilia of obscure etiology is described in the present report. Three years after the diagnosis of eosinophilia, metastatic anaplastic carcinoma of unknown primary was detected. Differential diagnosis is disscussed briefly. It is stressed that patients with hypereosinophilia of unknown etiology must be screened for malignancy regularly during follow up.